Unknown emblem drawn directly on DB605 Engine

[Revi16]

I've worked in aviation maintenance for about 30 years and have done a little work on radials and Merlins.
It's just my opinion, but painting a symbol on the block to indicate a bad sparkplug doesn't make much sense.

Sparkplugs are pretty simple to change, as they need to be. If one was found to be bad you would just replace it.
If I was working the aircraft, I (and most mechanics) would identify the cyl. that was bad. No need to apply some type of symbol.

Regards,